Respirator filter canisters and method of filling same

ABSTRACT

A gas mask filter canister of varying shapes is filled by orienting the a fill opening to face upwardly, introducing into the fill opening a particulate filter material, and vibrating the filter canister at a frequency and amplitude, and for a time until a predetermined packing density is reached. The invention can be used to fill elliptical or other odd shaped filter canisters having a concave profiles to conform closely to the curvature of the wearer&#39;s face.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of International Application No.PCT/US03/12700, filed Apr. 24, 2003, which claims the benefit of U.S.Provisional Patent Application No. 60/319,206, filed Apr. 25, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to filter canister for gas masks. In one aspect,the invention relates to a method of filling a filter canister with aparticulate filter material. In another of its aspects, the inventionrelates to filling a filter cartridge having a concave profileconforming to the curvature of the wearer's face. In yet another of itsaspects, the invention relates to a filter canister for a gas maskwherein the canister has an oblong shape and a concave profile forconforming to the shape of a user's face.

2. Description of the Related Art

PCT Application No. US01/12545, published Oct. 25, 2001, discloses abayonet-type connector for connecting a removable filter to a gas mask.A filter canister having an oval shape is also disclosed, comprisingparallel planar inlet and outlet faces separated by a perimeter wall.

Conventional replaceable circular or elliptical gas mask filters withparallel planar inlet and outlet faces can be mounted to both sides ofthe mask to extend laterally outwardly of the mask. Such filterstypically comprise a folded paper or fabric particulate filter and agranulated carbon adsorption filter. Settling of adsorbent in gas maskfilters before or during use can result in localized areas in which thegas flow path through the adsorbent is shorter than through the bulk ofthe adsorbent. This results in increased air flow through a smallervolume of adsorbent with a consequent early breakthrough of contaminantmaterial. In order to maximize the density of the carbon granules andavoid settling and the introduction of uncontrolled flow channelsthrough the adsorption filter, the adsorbent (i.e. granulated carbon) istypically placed in the filter canister through a process of “raining”or “snow storm” filling the granules into the filter in such a way thatthe density of the adsorbent is maximized. In this method, the adsorbentdrops through a tube containing four to five metal wire screens with thesame face area as the container to be filled. The screen opening sizeand spacing is related to the particle size of the adsorbent beingfilled. No single particle has the opportunity to pass through the tubewithout hitting the screen wires. This effectively randomizes anduniformly distributes the particles across the surface of the containerbeing filled. The adsorbent is also structurally constrained with acompressive force. The “snow storm filling” process requires that theinlet and outlet faces be planar.

Filters having a concave profile to conform closely to the curvature ofthe wearer's face offer several advantages over conventional filtershaving planar inlet and outlet faces. However, the curvature of thefilter is not conducive to the conventional “snow storm filling” methodof placing the adsorbent in the filter canister, and can prevent theadsorbent from assuming a minimum required density. The “snow stormfilling” method is only applicable to an adsorbent bed which has auniform flat depth. The “snow storm filling” method is not effective fora conformal filter design having a carbon filter bed that has an arcuatecontour on the inlet and outlet faces with a constant bed depth betweenthem. In order to ensure a minimum required thickness of the adsorbentat a minimum required density, a greater thickness of adsorbent may beneeded as compared to a filter having planar inlet and outlet faces,increasing the cost of the filter.

SUMMARY OF THE INVENTION

The invention relates to a filter canister filled with a particulatefilter material having a desired packing density wherein the shape ofthe filter bed is defined at least in part by canister walls and thecanister has a fill opening through which the particulate material isintroduced into the canister. According to the invention, a method offilling the filter canister comprising the steps of orienting the filtercanister with the fill opening facing upwardly, introducing theparticulate filter material through the fill opening, and vibrating thefilter canister at a frequency and amplitude, and for a time until thedesired packing density is reached.

The introducing and vibrating steps take place sequentially orsimultaneously. The particulate filter can be any conventional filtermaterial and typically is selected from the group consisting ofactivated charcoals, zeolites, molecular sieves and alumina Theseparticulate materials are adsorbants. Preferably, the particulate filtermaterial is ASZM-TEDA carbon.

The vibrating step can have a number of variations that includevibrating the filter canister in a vertical direction, vibrating thefilter canister in one or more horizontal direction and combinationsthereof. Typically, the filter canister is vibrated in at least twomutually orthogonal directions and the filter canister is vibratedsequentially in the two mutually orthogonal directions. In a preferredembodiment of the invention, the maximum positive and negative lateralaccelerations coincide with the maximum downward vertical accelerationof the filter canister. Further, the lateral vibration frequency is inphase with the vertical vibrational frequency and is half its value. Thevibration preferably has a sinusoidal component. In one embodiment, thevibrating step comprises a resulting horizontal acceleration representedby a rotating vector that traverses 360° of rotation every cycle.

In another embodiment, the vibrational acceleration in the vertical andhorizontal directions is variable. In a preferred embodiment, thevibrational acceleration in horizontal direction is about 0.48 g and thevibrational acceleration in a vertical direction is about 0.45 g.Typically, the vertical acceleration of vibration is less than 1 g. In amost preferred embodiment of the invention, the particulate fillermaterial has an average diameter and the amplitude of vibration isapproximately equal to the average diameter of the particulate fillermaterial. In yet another embodiment, the vibrating step includesvibrating the filter canister in a horizontal direction while rotatingthe filter canister about a vertical axis.

The filter canister can take a number of shapes but in a preferredembodiment, it has a curved peripheral outer wall and the fill openingis in the peripheral outer wall. The filter canister can ellipticallyshaped or some other complex or irregular shape. In one embodiment, thecanister is further defined by an outlet wall that is concave to conformto the curvature of the face of the user. Further, the canister can havean inlet wall that is convex. The inlet wall and the outlet wall arespaced from each other and joined by the peripheral outer wall.Preferably, the shape of the filter bed is defined at least in part bythe canister walls.

The particulate filter material can be mixed with short heterophilfibers. Desirably, the heterophil fibers have a length of about 3-5 mm.The heterophil fibers have a core and an outer sheath, and the outersheath is formed of a polymer with a melting temperature less than thatof the core. The core is made of glass or a synthetic polymer. Thesynthetic polymer is preferably polyamide. In a preferred embodiment,the outer sheath polymer is ethylvinylacetate. The filled filter bed canbe heated to melt the outer sheath and then cooled to fuse the filledfilter bed into an immobilized shape.

The desired packing density of the particulate filter material is atleast 0.6 grams per cubic centimeter, preferably in the range of about0.60 to about 0.72 grams per cubic centimeter.

In a preferred embodiment, the filter cartridge has an oval shape, andthe particulate filter materials are 20×50 ASZM-TEDA carbon granules,the frequency of the vibration is about 60 Hz in a vertical directionand about 29 Hz in a horizontal direction.

Further according to the invention, a filter canister comprises ahousing formed by an inlet wall and an outlet wall that are spaced fromeach other and joined by a curved peripheral outer wall. The curvedperipheral outer wall has a fill opening that is closed by a plug. Theinlet and outlet walls having openings therein for passage of airtherethrough. A particulate filter material is in the housing and formsa filter element within the housing to filter air passing from the inletwall to the outlet wall.

In a preferred embodiment, the outer peripheral wall is a complex shape,for example, an oblong shape, such as an ellipse. In one embodiment, theoutlet wall is concave. In a preferred embodiment, the inlet wall isconvex.

Preferably, the particulate filter material has a packing density in therange of about 0.060 to 0.072 grams per cubic centimeter. Theparticulate filter material is selected from the group of activatedcharcoals, zeolites, molecular sieves and alumina, preferably, ASZM-TEDAcarbon.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an exploded perspective view of a gas mask with a filterassembly comprising a primary filter and an auxiliary filter accordingto the invention.

FIG. 2 is a perspective view of the primary filter of FIG. 1.

FIG. 3 is a schematic view of a vibrating table used in the filling ofthe primary filter of FIG. 2 with a granulated carbon adsorbentaccording to the invention.

FIG. 4 is a graphical representation of a relationship between vibrationfrequency and amplitude when a filter canister is subjected to avibrational acceleration of 1 g.

FIG. 5 is a graphical representation of an optimal weight of granulatedcarbon adsorbent for selected vertical and horizontal vibrationamplitudes at a fixed horizontal and a first vertical frequency.

FIG. 6 is a graphical representation of an optimal weight of granulatedcarbon adsorbent for selected vertical and horizontal vibrationamplitudes at a second vertical frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A gas mask assembly 10 comprising elliptically-shaped conformal filtersis shown in FIG. 1. The gas mask assembly 10 comprises a generallyconventional gas mask 12 and at least one laterally-extending filterassembly 14. The gas mask 12 comprises at least one filter mount 16 at alower lateral portion of the gas mask 12, comprising a self-sealingmechanism as disclosed in PCT application US01/12545, published Oct. 25,2001, and incorporated herein by reference in its entirety, and an inletport 20. A single filter assembly 14 is shown in FIG. 1 attached to asingle filter mount 16 on a first side of the gas mask 10.Alternatively, the filter assembly 14 can be mounted to a second side ofthe gas mask 10, or a pair of filter assemblies can be utilized. In thepreferred embodiment, the inlet port 20 can receive a bayonet connectionon the filter assembly 14 as disclosed in PCT Application No.US01/12545, although a threaded filter connector 30 can also beutilized, as shown on the filter assembly 14 in FIGS. 1 and 2. The gasmask 12 can also comprise a speech module 22 that combines the functionsof speech and drinking. Such a speech module is disclosed in U.S.Provisional Patent Application Ser. No. 60/306,333, filed Jul. 18, 2001.

The filter assembly 14 comprises a primary filter 24 and an auxiliaryfilter 26 adapted in a conventional manner for fluid interconnection andmounting to the gas mask filter mount 16.

Referring now to FIG. 2, the primary filter 24 comprises a gas maskfilter having a generally conventional design except for anelliptically-shaped canister 40 with a generally concave or arcuateoutlet wall for conforming the canister 40 to the curvature of thewearer's face. The canister 40 has a convex inlet wall 42 and a concaveoutlet wall 44 in parallel, spaced-apart relationship joined by aperipheral outside wall 46 to define an enclosed filter chamber (notshown) in which filter elements are retained. The outlet wall has a fillopening 62 at one end with a plug 64 sealed in the opening. At least onegenerally conventional particulate filter element (not shown) and atleast one generally conventional adsorption filter element (not shown)are retained within the filter chamber. The airflow through the filter40 can be axial or radial, passing into the canister 40 through inletopenings 48 in the inlet wall 42, through the particulate filter elementand the adsorption filter element, and exiting the canister 40 throughan aperture in the outlet wall 44 to enter the gas mask 12 through theinlet port 20. The primary filter 24 can have the general structure andarrangement of the particulate filter element and the adsorption filterelement as shown in PCT Application No. US01/12545, or other suitablefilter element structures and arrangements accommodating radial or axialflow through the filter 24.

The adsorption filter element comprises a granulated activated charcoalwhich can be impregnated with heavy metal salts such as copper, silver,zinc and molybdenum, and also with amine triethylenediamine, to provideprotection against airborne military chemical materials. Otherconventional impregnated charcoals or alumina suitable for militaryapplications can be used, as can non-impregnated charcoals for filtersto be used in industrial rather than military applications. As anexample, a copper sulfate-treated charcoal can be used for anenvironment containing ammonia.

The granulated charcoal that forms the adsorbent filter element isfilled in the filter chamber by a process of controlled vibrationfilling in order to achieve a minimum required density.

The process for placing the granulated charcoal into the filter will nowbe described with reference to FIG. 3. A suitably-sized orifice 62 isprovided in the outside wall 46 through which the charcoal granules 54are introduced from a hopper 52 while the canister 40 is operablysupported on a vibrating platform 50. FIG. 3 shows the filter canister40 in a schematic representation supported on a vibrating platform 50for imparting vertical and horizontal vibration to the canister 40 asthe canister 40 is filled with a granular adsorbent. However, anysuitable device can be utilized for imparting vertical and horizontalvibration to the canister 40 during filling, consistent with thevibration parameters hereinafter discussed.

The vibrating platform 50 can impart a variable-frequency,variable-amplitude vertical vibration 56 to the canister 40. Thevibrating platform 50 can also impart a variable-frequency,variable-amplitude first horizontal vibration 58 and avariable-frequency, variable-amplitude second horizontal vibration 60orthogonal thereto to the canister 40. The magnitudes of both horizontaland vertical forces are carefully controlled in order to impartsufficient energy into the charcoal granules to enable them to achievean optimum packing density of approximately 0.62 grams per cubiccentimeter for ASZM-TEDA carbon. The optimum packing density will varywith the particle density of each type of carbon. When filling iscomplete, a plug 64 is placed into the orifice and ultrasonically weldedto the outer side wall 46 to complete the enclosure of the granularadsorbent filter element. The vertical and horizontal vibrations 56-60can be independently varied to optimize the density of the granularadsorbent during the filling process.

Vibration Theory

The vibration parameters of frequency, amplitude, time, and direction inorder to achieve an optimum density of a particulate material are basedupon well-known theory. If the filter is vibrated vertically andsinusoidally during filling, then the adsorbent particles willexperience varying effective weights as a function of time, vibrationamplitude and vibration frequency. The equations of motion are developedstarting with the following definitions:

-   -   A: Maximum half-cycle travel, in feet (amplitude)    -   a: Instantaneous filter acceleration at any time, in        feet/second²    -   f: Frequency, in cycles/second    -   g: Acceleration of gravity=32.174 feet/second²    -   n: Any integer from 0 to ∞    -   t: Time, in seconds    -   v: Instantaneous filter velocity at any time, in feet/second    -   z: Instantaneous filter vertical position at any time, in feet

The relevant equations are:

1.  z = A ⋅ sin (2 ⋅ π ⋅ f ⋅ t)${2.\mspace{14mu} v} = {\frac{\mathbb{d}z}{\mathbb{d}t} = {A \cdot 2 \cdot \pi \cdot f \cdot {\cos\left( {2 \cdot \pi \cdot f \cdot t} \right)}}}$${3.\mspace{14mu} a} = {\frac{\mathbb{d}v}{\mathbb{d}t} = {{- A} \cdot \left( {2 \cdot \pi \cdot f} \right)^{2} \cdot {\sin\left( {2 \cdot \pi \cdot f \cdot t} \right)}}}$${4.\mspace{14mu}\frac{\mathbb{d}a}{\mathbb{d}t}} = {{{- A} \cdot \left( {2 \cdot \pi \cdot f} \right)^{3} \cdot {\cos\left( {2 \cdot \pi \cdot f \cdot t} \right)}} = 0}$5.  0 = cos (2 ⋅ π ⋅ f ⋅ t)and, therefore,2·π·f·t=0.5π+nπ  5a.a=g=32.174ft/s ² =−A·(2·π·f)²·sin(0.5π+nπ)  6.32.174ft/s² =−A·(2·π·f)²  7.

Equation 1 defines the vertical position of a vibrating filter as afunction of time and of the vibration frequency and amplitude. Equation2 reflects the fact that filter velocity is the derivative of positionwith respect to time. Equation 3 defines filter acceleration as thederivative of the velocity with respect to time. Equation 4 is used todetermine when the filter vertical acceleration is at a minimum ormaximum value. This will occur whenever the derivative of accelerationwith respect to time, equation 5, is zero. For the trivial case wheneither frequency or time is zero, the maximum and minimum accelerationis also zero. For all other cases, the minimum and maximum accelerationsoccur when the cosine function is zero, as shown in equation 5. Thisoccurs every half cycle (180°) starting at 0.571 radians (90°). Themagnitude of the acceleration is the same for the minimum and maximum,but the directions are opposite, i.e. positive or upward for the maximumand negative or downward for the minimum. The adsorbent experiences thegreatest effective reduction in weight when the filter is acceleratingat its maximum downward value. This is the condition at which it isdesirable to apply the maximum lateral force to the filter in order tomove the adsorbent particles into their most stable position. Thiscondition occurs every time n is an even integer and the sine functionin equations 1, 3 and 6 equals +1. Empirical data indicates thattightest packing is achieved at less than fluidization flow, thusoptimum maximum vertical acceleration will be less than 1 g. Equation 7defines the upper limit on vertical acceleration at 1 g. Correspondingvalues of amplitude and frequency are shown in FIG. 4.

For optimum packing of adsorbent, the filters must be vibratedvertically at some frequency and amplitude combination below the curvedline 70 shown in FIG. 4. Empirical data does not yet exist from which todetermine the optimum lateral vibration to move the individual particlesinto their optimum locations, but can be experimentally determined. Itis anticipated that the maximum lateral acceleration would be 1 g orless and that the optimum amplitude would be approximately equal to theparticle diameter. Optimal acceleration for filling will typically beless than 1 g, The maximum positive and negative lateral accelerationsshould occur at the same time as the maximum downward verticalacceleration. Thus, the lateral vibration frequency must be in phasewith the vertical frequency and exactly half its value. The preferredembodiment of the lateral vibrators comprises two lateral vibratorspositioned 90° apart. These vibrators should be actuated alternately,since simultaneous operation would result in motion in a singledirection as determined by vector addition of their operation.Alternately, one lateral vibrator can be used while continuouslyrotating the filter during filling. In yet another embodiment, arotating horizontal vibrator can be used.

A rotating horizontal vibrator has the advantage that a particle may bemoved in any horizontal direction as long as the horizontal and verticalfrequencies are not the same. The maximum downward acceleration willoccur at a different horizontal direction for each cycle when thefrequencies are not identical.

The object of the vibrational filling technique is to provide sufficientenergy to move particles from less dense positions to more densepositions without removing particles from the more dense positions.Particle shape is the factor in minimizing the tendency of a particle tomove out of a dense configuration during vibration. With the volume ofthe voids between the particles minimized, resulting in a greaterpacking density, the particle will be more difficult to dislodge. Theseproperties will improve the more closely the shape of the particlematches the shape of the depression into which it falls.

Vibrational filling is sensitive to fill rate. Each subsequent layer ofparticles restricts the movement of the particles below and “locks” theminto place. The fill rate must allow each layer of particles sufficienttime to settle into place. This has particular ramifications for aconformal filter, because the cross-sectional area being filledincreases from zero to a constant value at the beginning of the fillingprocess and then decreases to a small value at the end of the fillingprocess.

Empirical Development

Experimental testing was conducted to evaluate the feasibility ofvibrational adsorbent packing and to indicate approaches foroptimization of the method.

A baseline was established by “snow storm” filling a 1,000 ml graduatedcylinder with 510.56 grams of 20×50 ASZM-TEDA carbon.

A dual axis vibration table was utilized having a usable test surface of3″×6″. Vibration force was independently adjustable in the vertical andhorizontal directions. However, horizontal vibration greater than 1 gforce generated vertical vibrations in the test surface that interferedwith some of the tests. A single waveform generator supplied the basevibration signal so that vertical and horizontal vibrations wereidentical in frequency, phase and sinusoidal waveform. Seventeen testswere completed using a standard graduated cylinder. The best vibrationalpacking density achieved was identical to the best “snow storm” fillingresults. This condition occurred at a vibrational frequency of 24.7 Hz,vertical acceleration of 0.35 g and a horizontal acceleration of 1.0 g.

Subsequent testing was done utilizing various versions of vibrationtables specifically designed to allow independent control of verticaland horizontal frequencies and amplitudes. The horizontal vibration wasforced by a variable speed motor with a weight positioned a fixeddistance from the motor shaft. The motor was attached vertically to thehorizontal vibrating plate of the vibration table so that the weightrotated in the horizontal plane. The vertical position of the weight wasadjusted to minimize the vertical component of the horizontal vibration,but this vertical component remained significant. The resultinghorizontal acceleration comprised a rotating vector which traversed 360°of rotation every cycle. This mode of vibration can be expected toprovide better results that a one or two-direction horizontalacceleration, as previously discussed.

Vertical acceleration of the horizontal plate was provided by anelectromagnet mounted under the center of the plate. This arrangementcreated a small, unwanted horizontal vibration component.

FIG. 5 shows the results of testing using a non-conformal (flat), ovalshaped filter using 20×50 ASZM-TEDA carbon granules, with a 60 Hzvertical vibration, a 29 Hz horizontal vibration, and variable verticaland horizontal acceleration. Maximum carbon granule density 72 wasachieved for these conditions at a horizontal acceleration of 0.48 g andvertical acceleration of 0.45 g.

FIG. 6 shows the results for vibrationally filling a conformal filterwhen the horizontal and vertical frequencies are almost identical, i.e.a 30 Hz vertical vibration and a 29 hertz horizontal vibration. As shownin FIG. 6, vertical and horizontal acceleration were also varied. Thetest results indicate that the packing density is less than that of“snow storm” filling, represented by line 74, is optimized by utilizinga higher horizontal amplitude, and is less dependent on verticalamplitude at the higher horizontal amplitude.

The vibrational filling method for an elliptical, conformal, granulatedcarbon adsorption filter disclosed herein solves the problems ofinadequate and inconsistent adsorbent density, and settling of theadsorbent material during use of the filter, experienced with anelliptical, conformal, granulated carbon filter prepared using aconventional “snow storm filling” method. This enables elliptical,conformal gas mask filters to be economically fabricated, therebyimproving the functionality of a conventional gas mask by conforming theprimary filter 24 to the curvature of the wearer's face, andstreamlining the profile of the gas mask 12 and filter assembly 14. Thestreamlined profile reduces the potential that the filters 24, 26 willinterfere with the wearer's vision and activities (e.g. sighting afirearm), or contact objects in close proximity to the wearer,potentially damaging the filter assembly 14 and rendering itinoperative, and injuring the wearer. The improved method ofmanufacturing adsorption filter elements provides the desired filteringcapability of a granulated activated charcoal filter in an elliptical,conformal filter.

While the invention has been specifically described in connection withcertain specific embodiments thereof, it is to be understood that thisis byway of illustration and lot of limitation. Reasonable variation andmodification are possible within the scope of the foregoing drawings anddescription without departing from the spirit of the invention.

1. A method of filling a filter canister with a particulate filtermaterial to a desired packing density wherein the canister has a fillopening through which the particulate filter material is introduced intothe canister, the method comprising the steps of: orienting the filtercanister with the fill opening facing upwardly; introducing theparticulate filter material through the fill opening; and vibrating thefilter canister at a frequency and amplitude, and for a time until thedesired packing density is reached; wherein the vibrating step includesvibrating the filter canister in a vertical direction with a verticalvibrational frequency that includes imparting a maximum downwardvertical acceleration to the filter canister; wherein the vibrating stepincludes vibrating the filter canister in a horizontal direction with alateral vibration frequency, wherein the filter canister has maximumpositive and negative accelerations in the horizontal direction; whereinthe horizontal vibration frequency is in phase with the verticalvibrational frequency and is half its value.
 2. A method of filling afilter canister according to claim 1 wherein the introducing andvibrating steps take place sequentially.
 3. A method of filling a filtercanister according to claim 1 wherein the introducing and vibratingsteps take place simultaneously.
 4. A method of filling a filtercanister according to claim 1 wherein the particulate filter material isselected from the group of activated charcoals, zeolites, molecularsieves and alumina.
 5. A method of filling a filter canister accordingto claim 1 wherein the particulate material is an adsorbent.
 6. A methodof filling a filter canister according to claim 1 wherein the vibratingstep includes vibrating the filter canister in multiple horizontaldirections.
 7. A method of filling a filter canister according to claim6 wherein the maximum positive and negative accelerations in thehorizontal direction coincide with the maximum downward verticalacceleration of the filter canister.
 8. A method of filling a filtercanister according to claim 1 wherein the vibrating step includesvibrating the filter canister in at least two mutually orthogonaldirections.
 9. A method of filling a filter canister according to claim8 wherein the filter canister is vibrated sequentially in the twomutually orthogonal directions.
 10. A method of filling a filtercanister with a particulate filter material to a desired packing densitywherein the canister has a fill opening through which the particulatefilter material is introduced into the canister, the method comprising:orienting the filter canister with the fill opening facing upwardly;introducing the particulate filter material through the fill opening;and vibrating the filter canister at a frequency and amplitude, and fora time until the desired packing density is reached; wherein the filtercanister has a curved peripheral outer wall and the fill opening is inthe peripheral outer wall.
 11. A method of filling a filter canisteraccording to claim 10 wherein the outer wall of the filter canister iselliptically shaped.
 12. A method of filling a filter canister accordingto claim 11 wherein the peripheral outer wall defines an irregularshape.
 13. A method of filling a filter canister according to claim 10wherein the canister is further defined by an outlet wall that isconcave to conform to the curvature of the face of the user.
 14. Amethod of filling a filter canister according to claim 13 wherein thecanister is further defined by an inlet wall that is convex, and theinlet wall and the outlet wall are spaced from each other and joined bythe peripheral outer wall.
 15. A method of filling a filter canisterwith a particulate filter material to a desired packing density whereinthe canister has a fill opening through which the particulate filtermaterial is introduced into the canister, the method comprising:orienting the filter canister with the fill opening facing upwardly;introducing the particulate filter material through the fill opening;and vibrating the filter canister at a frequency and amplitude, and fora time until the desired packing density is reached; wherein theparticulate material is mixed with short heterophil fibers.
 16. A methodof filling a filter canister according to claim 15 wherein theheterophil fibers have a length of about 3-5 mm.
 17. A method of fillinga filter canister according to claim 15 wherein the heterophil fibershave a core and an outer sheath, and the outer sheath is formed of apolymer with a melting temperature less than that of the core.
 18. Amethod of filling a filter canister according to claim 17 wherein thecore is made of glass or a synthetic polymer.
 19. A method of filling afilter canister according to 18 wherein the synthetic polymer ispolyamide.
 20. A method of filling a filter canister according to claim17 wherein the outer sheath polymer is ethylvinylacetate.
 21. A methodof filling a filter canister according to claim 17 and furthercomprising the steps of heating the filled filter bed to melt the outersheath and cooling the filter bed to fuse the filled filter bed into animmobilized shape.
 22. A method of filling a filter canister with aparticulate filter material to a desired packing density wherein thecanister has a fill opening through which the particulate filtermaterial is introduced into the canister, the method comprising thesteps of: orienting the filter canister with the fill opening facingupwardly; introducing the particulate filter material through the fillopening; and vibrating the filter canister at a frequency and amplitude,and for a time until the desired packing density is reached; wherein thevibrating step includes vibrating the filter canister in a verticaldirection that includes a vertical acceleration and wherein the verticalacceleration of vibration is less than 1 g.
 23. A method of filling afilter canister according to claim 22 wherein the maximum amplitude ofany vibration for a given frequency in the vertical direction is definedby the equation:A=g/(2πf)² where: A is the amplitude in feet, g is the acceleration ofgravity in feet/second² and f is the frequency in cycles/second.
 24. Amethod of filling a filter canister according to claim 22 wherein thefilter material forms a filter bed within the canister, the canister isformed with a side walls an inlet wall and an outlet wall, and the shapeof the filter bed is defined at least in part by the canister side,inlet and outlet walls.
 25. A method of filling a filter canister with aparticulate filter material to a desired packing density wherein thecanister has a fill opening through which the particulate filtermaterial is introduced into the canister, the method comprising thesteps of: orienting the filter canister with the fill opening facingupwardly; introducing the particulate filter material through the fillopening; and vibrating the filter canister at a frequency and amplitude,and for a time until the desired packing density is reached; wherein thedesired packing density is at least 0.6 grams per cubic centimeter andthe particulate filter material is ASZM-TEDA carbon.
 26. A method offilling a filter canister with a particulate filter material to adesired packing density wherein the canister has a fill opening throughwhich the particulate filter material is introduced into the canister,the method comprising the steps of: orienting the filter canister withthe fill opening facing upwardly; introducing the particulate filtermaterial through the fill opening; and vibrating the filter canister ata frequency and amplitude, and for a time until the desired packingdensity is reached; wherein the maximum amplitude of any vibration forany given frequency of vibration of the filter canister is defined bythe equation:A=g/(2πf)² where: A is the amplitude in feet, g is the acceleration ofgravity in feet/second² and f is the frequency in cycles/second.
 27. Amethod of filling a filter canister according to claim 26 wherein thevibration has a sinusoidal component.
 28. A method of filling a filtercanister according to claim 26 wherein the vibrating step includesvibrating the filter canister in a horizontal direction while rotatingthe filter canister about a vertical axis.
 29. A method of filling afilter canister according to claim 26 wherein the vibrational frequencyis about 24.7 Hz, the vertical acceleration is about 0.35 g and thehorizontal acceleration is about 1.0 g.
 30. A method of filling a filtercanister according to claim 26 wherein the vibrating step comprises aresulting horizontal acceleration represented by a rotating vector whichtraverses 360° of rotation every cycle.
 31. A method of filling a filtercanister with a particulate filter material to a desired packing densitywherein the canister has a fill opening through which the particulatefilter material is introduced into the canister, the method comprisingthe steps of: orienting the filter canister with the fill opening facingupwardly; introducing the particulate filter material through the fillopening; and vibrating the filter canister at a frequency and amplitude,and for a time until the desired packing density is reached; the filtercartridge has an oval shape, and the particulate filter materials are20x50 ASZM-TEDA carbon granules, the frequency of the vibration is about60 Hz in a vertical direction and about 29 Hz in a horizontal direction.32. A method of filling a filter canister according to claim 31 whereinthe vibrations in the vertical and horizontal direction haveacceleration in each direction and the vibrational acceleration in thevertical and horizontal directions is variable.
 33. A method of fillinga filter canister according to claim 31 wherein the vibrationalacceleration in horizontal direction is about 0.48 g and the vibrationalacceleration in a vertical direction is about 0.45 g.
 34. A method offilling a filter canister according to claim 31 wherein the desiredpacking density is between about 0.60 and 0.72.
 35. A method of fillinga filter canister with a particulate filter material to a desiredpacking density wherein the canister has a fill opening through whichthe particulate filter material is introduced into the canister, themethod comprising the steps of: orienting the filter canister with thefill opening facing upwardly; introducing the particulate filtermaterial through the fill opening; and vibrating the filter canister ata frequency and amplitude, and for a time until the desired packingdensity is reached; wherein the particulate filler material has anaverage diameter and the amplitude of vibration is approximately equalto the average diameter of the particulate filler material.
 36. A methodof filling a filter canister according to claim 35 wherein thevibrational acceleration is less than 1 g.
 37. A method of filling afilter canister with a particulate filter material to a desired packingdensity wherein the canister has a fill opening through which theparticulate filter material is introduced into the canister, the methodcomprising the steps of: orienting the filter canister with the fillopening facing upwardly; introducing the particulate filter materialthrough the fill opening; and vibrating the filter canister at afrequency and amplitude, and for a time until the desired packingdensity is reached; wherein the canister is further defined by an outletwall that is concave to conform to the curvature of the face of theuser.
 38. A method of filling a filter canister according to claim 37wherein the vibrating step includes vibrating the filter canister in ahorizontal direction.
 39. A method of filling a filter canisteraccording to claim 38 wherein the vibrating step includes vibrating thefilter canister in multiple horizontal directions.
 40. A method offilling a filter canister according to claim 37 wherein the canister isfurther defined by an inlet wall that is convex, and the inlet wall andthe outlet wall are spaced from each other and joined by a peripheralouter wall.